Functional significance of an ITGAM polymorphism in SLE

描述（由申请人提供）：最近的自身免疫全基因组关联研究已经发现ITGAM编码区多态性（R77H）与SLE相关，ITGAM是编码CD11b整合素分子1链的基因。ITGAM多态性与不同种族的SLE相关，并且随着SLE肾炎发病率的增加，疾病严重程度也会增加。我们实验室最近的研究表明，在三种不同的SLE模型中，常驻肾巨噬细胞CD11b表达的增加与肾炎的发作有关，并且这种表型会随着临床缓解而逆转。ITGAM在人SLE肾活检中也过表达。由于ITGAM具有多种促炎功能，因此我们假设与SLE相关的ITGAM多态性导致功能增强，从而增加单核细胞的粘附、促炎或促凝功能。为了验证这一假设，我们将利用一个独特的非常大的正常受试者注册表，其中包含来自正常受试者的DNA，这些受试者表示愿意重新联系以参与各种研究方案。我们将选择纯合的R/R和H/H个体进行研究。为了确定两个多态ITGAM等位基因的功能差异，我们将确定R77H ITGAM多态性是否会改变CD11b的表达或配体结合特性。我们将确定多态性是否会影响表达CD11b的单核细胞在吞噬、粘附、迁移和炎症分子产生方面的功能。最后，我们将建立携带多态性等位基因的转染细胞系，以更好地研究流动条件下的粘附和下游信号转导事件。这些研究将有助于我们确定ITGAM多态性的功能意义，并可能使我们了解这种多态性如何影响SLE的易感性和严重程度。

DESCRIPTION (provided by applicant): Recent genome-wide association studies in autoimmunity have identified the association of a coding region polymorphism (R77H) of ITGAM, a gene that encodes for the 1 chain of the CD11b integrin molecule, with SLE. The ITGAM polymorphism is associated with SLE across ethnic groups and also confers increased disease severity with an increased incidence of SLE nephritis. Recent studies from our laboratory have shown that increased expression of CD11b on resident renal macrophages is associated with nephritis onset in three different SLE models and that this phenotype reverses concomitant with clinical remission. ITGAM is also overexpressed in human SLE renal biopsies. Since ITGAM has multiple pro-inflammatory functions we therefore hypothesize that the ITGAM polymorphism associated with SLE results in a gain of function such that there is increased adhesion, pro-inflammatory or pro-coagulant function of monocytes. To test this hypothesis we will utilize a unique very large normal subject registry containing DNA from normal subjects who express a willingness to be re-contacted to participate in various research protocols. We will select homozygous R/R and H/H individuals for our study. To identify functional differences in the two polymorphic ITGAM alleles we will establish whether the R77H ITGAM polymorphism alters expression or ligand binding characteristics of CD11b. We will determine whether the polymorphism affects the function of monocytes expressing CD11b with respect to their phagocytosis, adhesion, migration and their production of inflammatory molecules. Finally, we will establish transfected cell lines bearing the polymorphic alleles to better study adhesion under flow conditions and downstream signal transduction events. These studies should help us identify the functional significance of the ITGAM polymorphism and may allow us to understand how this polymorphism affects the susceptibility to and severity of SLE. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to determine the functional significance of the R77H coding region polymorphism in the ITGAM gene that is associated with human SLE. ITGAM encodes the alpha chain of the CD11b adhesion molecule expressed on leukocytes and monocytes. The approach will be to use peripheral blood normal individuals homozygous for the two allelic forms of ITGAM to analyze the expression of CD11b and the function of monocytes with respect to adhesion, migration and expression of pro-inflammatory molecules.